NSFAS NOT APPRECIATING STUDENTS THAT ARE PAYING BACK THE MONEY

I have been NSFAS since 2009 and in 2017 I decided to pay an extra, they debit me the whole amount and I paid an extra. When I got their statement they debit order amount was less than the one that went out of my account, I went to the bank in 2017 to get bank statement, I emailed it to them to show how much was debited from my account so they can allocate payments accordingly, I did my follow ups from 2017 to 2019 still my payments are still not allocated correctly. That time they are charging me ridiculous amount of interest. I need my payments allocated correctly cant believe they employ such *********** people, how many times must one follow up before their queries can be attended to and I want that interest charged from 2 ********** to be reversed and charge correct interest. I want to finish off paying that account, now I cant even pay extra because they don't allocate payment accordingly